The ultrastructure of bone, intestinal mucosa and other tissues will be observed by methods which minimize the restructuring of the tissue components. These methods include ultracryotomy and ultramicroincineration. Comparisons will be made between normal and pathological conditions in laboratory animals (rats, chickens, quail) induced by nutritional deficiencies and hormonal treatment. We will attempt to develop non-aqueous staining methods for the ultracryotomy specimens to better visualize the subcellular structure. In addition, the osteogenic response in avian species to estrogen will be studied particularly in relationship to the decrease in hematopoeitic activity that accompanies the osteogenic response. BIBLIOGRAPHIC REFERENCES: Miller, A.L. and Schraer, H.: Ultrastructural Observations of Amorphous Bone Mineral in Avian Bone. Calcif. Tiss. Res. 18:311-324 (1975). Gay, C.V. and Schraer, H.: Frozen Thin-Sections of Rapidly Forming Bone: Bone Cell Ultrastructure. Calcif. Tiss. Res. 19:39-49 (1975).